kbuild: compress the kernel with pigz if available

The gzip step of a kernel build is very lengthy, especially for larger
builds such as allmodconfig.

gzip itself cannot be run in parallel, however

kbuild: compress the kernel with pigz if available

The gzip step of a kernel build is very lengthy, especially for larger
builds such as allmodconfig.

gzip itself cannot be run in parallel, however an alternative tool exists
that can, providing the same feature set as gzip itself - pigz - which
works as a drop-in replacement.

On a 128-core Threadripper, gzip -9 of a 36 MiB x86-64 vmlinux.bin takes
1.6s, and with pigz it takes 0.09s, so the performance increase is
significant.

Therefore introduce the KPGZIP build variable which specifies the
compressor to use for the kernel image and default it to pigz if available,
or KGZIP otherwise (which itself defaults to gzip).

Modules, packaging and the embedded kernel configuration (CONFIG_IKCONFIG)
continue to use KGZIP which defaults to a single-threaded gzip instance.

Module compression is run in parallel by make, so pigz offers no benefit
there, packaging sits outside the build and the embedded configuration is
too small to matter.

pigz is executed using scripts/jobserver-exec, which reserves the job slots
make has free - necessary, as otherwise pigz would just grab unbounded
CPUs.

The kernel image compression step is always performed at the end of the
build so should typically have all job slots available.

pigz always provides byte-for-byte identical output across runs regardless
of thread count, but pigz and gzip are not guaranteed to generate the same
binary output, so reproducible builds must use the same tools consistently.

Also update Documentation/kbuild/kbuild.rst to describe KPGZIP and
Documentation/process/changes.rst to list the optional pigz dependency.

While there, add entries for the other compressor programs.

Finally, update scripts/ver_linux to include the pigz version there.

Every x86 build ends with the compression of vmlinux.bin, 36MB for
defconfig and over 200MB for allmodconfig, no-op builds are unchanged.

Whole build, 128-thread Threadripper 9980X, best of N runs:

before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 7.7s 6.0s -1.7s (-22%)
x86 defconfig, touch mm/vma.c, clang 6.9s 5.4s -1.5s (-21%)
x86 defconfig, clean, gcc 28.2s 26.3s -1.8s (-6%)
x86 defconfig, clean, clang 28.7s 27.2s -1.5s (-5%)
x86 allmodconfig, touch mm/vma.c, gcc 23.7s 15.4s -8.3s (-35%)
x86 allmodconfig, touch mm/vma.c, clang 22.5s 15.6s -7.0s (-31%)
x86 allmodconfig, clean, gcc 294.1s 278.6s -15.5s (-5%)
x86 allmodconfig, clean, clang 283.9s 266.8s -17.1s (-6%)

Suggested-by: Kees Cook <kees@kernel.org>
Link: https://zlib.net/pigz/
Assisted-by: LLM
Reviewed-by: Manuel Ebner <manuelebnerli@mailbox.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Link: https://patch.msgid.link/20260923-build-speedup-v4-22-73128809a4a4@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

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scripts/jobserver-exec: propagate child exit status

main() called JobserverExec().run() and discarded its return value,
then the script exited with the implicit status 0. As a result, any
Makefile t

scripts/jobserver-exec: propagate child exit status

main() called JobserverExec().run() and discarded its return value,
then the script exited with the implicit status 0. As a result, any
Makefile that wired a build step through jobserver-exec saw the step
silently succeed even when the wrapped command had failed.

Two in-tree callers were affected:

Documentation/devicetree/bindings/Makefile
cmd_chk_style runs a python checker via jobserver-exec and uses
"&& touch $@ || true" so failures leave the stamp file untouched
and the next make rerun reports them again. The swallowed exit
code made the stamp file get created even on failure, caching the
failed run and hiding the reported issues until the inputs change.

scripts/Makefile.vmlinux_o
cmd_gen_initcalls_lds runs scripts/generate_initcall_order.pl via
jobserver-exec; a perl failure was masked by the wrapper.

Return the subprocess exit code from main() and pass it to sys.exit()
so the wrapped command's status reaches make.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://patch.msgid.link/660368ca16e2d3845577a9fd157d2f37f0e09e85.1779908995.git.daniel@makrotopia.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

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docs: Move the python libraries to tools/lib/python

"scripts/lib" was always a bit of an awkward place for Python modules. We
already have tools/lib; create a tools/lib/python, move the libraries
t

docs: Move the python libraries to tools/lib/python

"scripts/lib" was always a bit of an awkward place for Python modules. We
already have tools/lib; create a tools/lib/python, move the libraries
there, and update the users accordingly.

While at it, move the contents of tools/docs/lib. Rather than make another
directory, just put these documentation-oriented modules under "kdoc".

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251110220430.726665-2-corbet@lwn.net>

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scripts/jobserver-exec: add a help message

Currently, calling it without an argument shows an ugly error
message. Instead, print a message using pythondoc as description.

Signed-off-by: Mauro Carva

scripts/jobserver-exec: add a help message

Currently, calling it without an argument shows an ugly error
message. Instead, print a message using pythondoc as description.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Message-ID: <64b0339eac54ac0f2b3de3667a7f4f5becb1c6ae.1758196090.git.mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

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scripts/jobserver-exec: move its class to the lib directory

To make it easier to be re-used, move the JobserverExec class
to the library directory.

Signed-off-by: Mauro Carvalho Chehab <mchehab+hua

scripts/jobserver-exec: move its class to the lib directory

To make it easier to be re-used, move the JobserverExec class
to the library directory.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Message-ID: <6be7b161b6c005a9807162ebfd239af6a4e6fa47.1758196090.git.mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

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scripts/jobserver-exec: move the code to a class

Convert the code inside jobserver-exec to a class and
properly document it.

Using a class allows reusing the jobserver logic on other
scripts.

Whil

scripts/jobserver-exec: move the code to a class

Convert the code inside jobserver-exec to a class and
properly document it.

Using a class allows reusing the jobserver logic on other
scripts.

While the main code remains unchanged, being compatible with
Python 2.6 and 3.0+, its coding style now follows a more
modern standard, having tabs replaced by a 4-spaces
indent, passing autopep8, black and pylint.

The code allows using a pythonic way to enter/exit a python
code, e.g. it now supports:

with JobserverExec() as jobserver:
jobserver.run(sys.argv[1:])

With the new code, the __exit__() function should ensure
that the jobserver slot will be closed at the end, even if
something bad happens somewhere.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Message-ID: <4749921b75d4e0bd85a25d4d94aa2c940fad084e.1758196090.git.mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

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scripts: support GNU make 4.4 in jobserver-exec

Starting with GNU make 4.4, --jobserver-auth newly uses named
pipe (fifo) instead of part of opened file descriptors:
https://www.gnu.org/software/mak

scripts: support GNU make 4.4 in jobserver-exec

Starting with GNU make 4.4, --jobserver-auth newly uses named
pipe (fifo) instead of part of opened file descriptors:
https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html

Support also the new format.

Signed-off-by: Martin Liska <mliska@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

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scripts/jobserver-exec: parse the last --jobserver-auth= option

In the GNU Make manual, the section "Sharing Job Slots with GNU make"
says:

Be aware that the MAKEFLAGS variable may contain mult

scripts/jobserver-exec: parse the last --jobserver-auth= option

In the GNU Make manual, the section "Sharing Job Slots with GNU make"
says:

Be aware that the MAKEFLAGS variable may contain multiple instances
of the --jobserver-auth= option. Only the last instance is relevant.

Take the last element of the array, not the first.

Link: https://www.gnu.org/software/make/manual/html_node/Job-Slots.html
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

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scripts/jobserver-exec: Fix a typo ("envirnoment")

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: remove PYTHON variable

Python retired in 2020, and some distributions do not provide the
'python' command any more.

As in commit 51839e29cb59 ("scripts: switch explicitly to Python 3"),
we

kbuild: remove PYTHON variable

Python retired in 2020, and some distributions do not provide the
'python' command any more.

As in commit 51839e29cb59 ("scripts: switch explicitly to Python 3"),
we need to use more specific 'python3' to invoke scripts even if they
are written in a way compatible with both Python 2 and 3.

This commit removes the variable 'PYTHON', and switches the existing
users to 'PYTHON3'.

BTW, PEP 394 (https://www.python.org/dev/peps/pep-0394/) is a helpful
material.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

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docs, parallelism: Rearrange how jobserver reservations are made

Rasmus correctly observed that the existing jobserver reservation only
worked if no other build targets were specified. The correct a

docs, parallelism: Rearrange how jobserver reservations are made

Rasmus correctly observed that the existing jobserver reservation only
worked if no other build targets were specified. The correct approach
is to hold the jobserver slots until sphinx has finished. To fix this,
the following changes are made:

- refactor (and rename) scripts/jobserver-exec to set an environment
variable for the maximally reserved jobserver slots and exec a
child, to release the slots on exit.

- create Documentation/scripts/parallel-wrapper.sh which examines both
$PARALLELISM and the detected "-jauto" logic from Documentation/Makefile
to decide sphinx's final -j argument.

- chain these together in Documentation/Makefile

Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/lkml/eb25959a-9ec4-3530-2031-d9d716b40b20@rasmusvillemoes.dk
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20191121205929.40371-4-keescook@chromium.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

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